1. Field of the Invention
The invention relates to a voltage converter, more particularly to a voltage converter capable of outputting a stable output voltage.
2. Description of the Related Art
A conventional voltage converter is generally provided with a control device for adjusting an output voltage thereof. The control device is usually in the form of a pulse-width modulation (PWM) controller. However, the PWM controller generally includes a differential amplifier, a sawtooth generator, a Schmidt comparator, an AND gate and a level shifter/FET driver, thereby resulting in a relatively complex design and higher costs.
Therefore, the object of the present invention is to provide a voltage converter capable of outputting an output signal with a stable output voltage, the voltage converter having a relatively simple construction and being capable of being produced at a relatively low cost.
According to one aspect of the present invention, a voltage converter comprises:
a power stage having an input adapted to be connected to a power source, and an output for outputting an output signal to a load, the power stage including a voltage-controlled switching device connected between the input and the output, the voltage-controlled switching device having a control input for receiving a control signal, the voltage-controlled switching device being operable at a switch-ON mode, where the control signal is a high-level signal, and a switch-OFF mode, where the control signal is a low-level signal;
a comparator having a first input end for receiving a trigger signal, a second input end for receiving an input signal associated with the output voltage, and an output end connected to the control input of the voltage-controlled switching device, the comparator comparing the trigger signal received at the first input end and the input signal received at the second input end, and outputting the control signal at the output end in accordance with result of comparison, wherein the control signal is the high-level signal when the trigger signal is greater than the input signal, and wherein the control signal is the low-level signal when the trigger signal is less than the input signal; and
a trigger circuit having a first input port adapted to be connected to a reference voltage source for receiving a reference voltage, a second input port connected to the output end of the comparator for receiving the control signal, and an output port connected to the first input end of the comparator so as to supply the trigger signal to the comparator, the trigger circuit being operable such that the control signal becomes the high-level signal when the trigger signal reaches a first threshold voltage, and such that the control signal becomes the low-level signal when the trigger signal reaches a second threshold voltage greater than the first threshold voltage.
The trigger circuit enables the comparator to output a periodic pulse signal that serves as the control signal to enable the voltage-controlled switching device to be activated periodically such that the voltage converter generates the output signal with a stable output voltage.
According to another aspect of the present invention, there is provided a control device for generating a control signal in a voltage converter. The voltage converter includes a power stage that has an input connected to a power source, and an output for outputting an output signal to a load. The power stage includes a voltage-controlled switching device connected between the input and the output. The voltage-controlled switching device has a control input for receiving the control signal. The voltage-controlled switching device is operable at a switch-ON mode, where the control signal is a high-level signal, and a switch-OFF mode, where the control signal is a low-level signal. The control device comprises:
a comparator having a first input end for receiving a trigger signal, a second input end for receiving an input signal associated with the output signal, and an output end adapted to be connected to the control input of the voltage-controlled switching device, the comparator comparing the trigger signal received at the first input end and the input signal received at the second input end, and outputting the control signal at the output end in accordance with result of comparison, wherein the control signal is the high-level signal when the trigger signal is greater than the input signal, and wherein the control signal is the low-level signal when the trigger signal is less than the input signal; and
a trigger circuit having a first input port adapted to be connected to a reference voltage source for receiving a reference voltage, a second input port connected to the output end of the comparator for receiving the control signal, and an output port connected to the first input end of the comparator so as to supply the trigger signal to the comparator, the trigger circuit being operable such that the control signal becomes the high-level signal when the trigger signal reaches a first threshold voltage, and such that the control signal becomes the low-level signal when the trigger signal reaches a second threshold voltage greater than the first threshold voltage.
The trigger circuit enables the comparator to output a periodic pulse signal that serves as the control signal to enable the voltage-controlled switching device to be activated periodically such that the voltage converter generates the output signal with a stable output voltage.